Seven diseases are now known to be caused by expansions of triplet repeats. Four, including the subject of the present proposal, are caused by expansions of CAG repeats, coding for polyglutamine. These include Huntington's disease (HD), spinocerebellar ataxia type 1 (SCA-1), and spinal and bulbar muscular atrophy. All involve degeneration of differing, although overlapping, subsets of neurons. The most recently discovered CAG triplet repeat disease is dentatorubral and pallidoluysian atrophy (DRPLA or Smith's disease). The gene causing this disorder was identified as part of a screening program for triplet repeats in the principal investigator's laboratory (Li et al., 1993). Primer sequences published in our paper were used by two groups of Japanese investigators to demonstrate that triplet repeat expansion at this locus causes DRPLA. We now propose to clone the full length cDNA for this gene, which we are terming "Atrophin-1." We have found that it has an unusual alternating acidic and basic residue protein motif with homology to other proteins, which may shed light on its function. We will clone and sequence full length cDNAs for rat and human versions of the cDNA. We will study the expression of the Atrophin-1 mRNA in human and rat tissues, in development, and in tissues from patients with the disorder, using techniques of RNA blot analysis and in situ hybridization. Based on the predicted protein sequence, we will synthesize unique peptides, couple them to carrier proteins, and raise and affinity purify specific antibodies. We will use these for protein blot and immunohistochemical studies to define the cellular and tissue localization of the Atrophin-1 protein. These studies will be carried out in parallel with ongoing studies in the PI's lab of the HD gene product. Together these studies should shed light on genes involved in these neurodegenerative disorders.